There are many occasions where an annular space between relatively moving tubulars can fill up with debris. In one case before cementing a liner that has been hung off an existing tubular through an inner running string, the inner running string is picked up far enough to determine that it is no longer secured to the liner so that after the cement job is done there are assurances that the inner running string will free to remove to the surface. Typically the inner running string is lifted a meter or more. During this lifting event debris that is in the vicinity can fall into the annular space between the liner and the running string. To combat this problem in the past debris barriers have been proposed which are basically annular shapes around the inner running string. Early efforts simply fixed the annular shape to the inner running string but this proved ineffective since on lifting the inner running string to make sure that there was release from the liner resulted in lifting the debris barrier too high and out of the liner tieback extension so that debris could still get into the annular gap between the running tools and the liner. Once debris gets into that gap there is a great chance that it may cause the inner running string to remain engaged to the liner via frictional forces or hydraulic locking the inner running string to the liner. If that happened a significant loss of time and cost in clearing the inner running string from the liner ensued and in some instances the inner running string could not be retrieved and sidetracking was then required.
From that point the focus shifted to ways to make the barrier effective downhole despite the significant amount of relative movement that takes place when confirming that the inner running string has released from the liner. In US Publication 2011/0108266 the debris barrier 7 is allowed to “float” on fluid introduced to an annular chamber below before the device is run in the hole. The problem with this design is that the debris can adhere the debris barrier to the lift mandrel that it surrounds with the unintended result of lifting the floating debris barrier away from its pool of fluid that was supposed to keep the barrier essentially stationary as the mandrel is lifted.
Other approaches touted the “hydraulic lock” where an elaborate system of seals to retain a volume of hydraulic fluid was used in an effort to keep the debris barrier in place. Such designs are illustrated in U.S. Pat. No. 6,408,945 (items 152 or 252) or U.S. Pat. No. 5,528,366 which is along the same line by the same inventor. The problems with this design are cost and reliability. The debris barrier had to have an internal reservoir that was initially filled at the surface and then used a network of seals to seal against the liner tieback extension so as to be able to maintain the liquid lock when the lift mandrel was lifted. Getting all these seals to effectively seal was key to the operation of the lock. However, there is the local debris issue and getting the seals to fit closely to the liner tieback extension that all could contribute to the loss of locking force. Finally the debris could wedge the barrier to the lift nipple to then put stress on the seals to hold the ever rising pressure if tandem movement occurred which could blow out a seal before surface personnel had any clue that such failure had occurred. In touting the hydraulic lock these references eschewed mechanical locking as undesirable and impractical in this application.
The present invention is a mechanical lock for the debris barrier. The barrier is locked when run in and remains locked as the lift nipple is raised. After a predetermined lifting the lock is defeated to allow the inner running string to be removed while capturing the debris barrier. Preferred designs of dogs and collets are disclosed. Those skilled in the art will gain a better understanding of these and other aspects of the invention from a review of the description of the preferred embodiment and associated drawings while recognizing that the full scope of the invention is to be determined by the appended claims.